<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container {
            width: 500px;
            height: 500px;
            background-color: rebeccapurple;
            clip-path: circle(50% at 0 0);
            transition: all .7s;
        }

        .container:hover {
            clip-path: circle(100%);
        }
    </style>
</head>

<body>
    <div class="container"></div>
</body>

</html>